1. Field of the Invention
The present invention relates to a color filter device and, more particularly, it relates to a color filter device which serves as a color filter having a new filtering characteristic by utilizing existing color filter material.
2. Description of the Background Art
FIG. 7 is a diagram showing a construction of a color temperature sensor incorporated in a sensing auto white balance device for a camera to which a conventional color filter device is applied.
In this color temperature sensor E, a red color filter element 1R, a green color filter element 1G and a blue color filter element 1B are provided in pairs with photodiodes 2R, 2G and 2B, respectively, as shown in FIG. 7. Incident light passes the color filter elements 1R, 1G, 1B to the photodiodes 2R, 2G, 2B. The photodiodes 2R, 2G, 2B photoelectrically transfer the incident light into a photoelectric current. A cathode and an anode of the photodiodes 2R, 2G, 2B are individually connected to a noninverting input terminal (+) and an inverting input terminal (-) of operational amplifiers 3. Each of the operational amplifiers 3 should have a sufficiently high input impedance in impedance characteristic so that the input bias current is sufficiently small to the photoelectric current. A diode 4 is connected between the output terminal and the inverting input terminal of the operational amplifier 3 for logarithmically compressing the photoelectric current and transferring it into voltage. A constant voltage source 5 is connected to the noninverting input terminal (+) of the operational amplifier 3 for setting a reference voltage in logarithmically compressing the photoelcrtic current and transferring it into voltage while output terminals 6R, 6G, 6B are connected to the output terminals of the operational amplifiers 3 for outputting voltages generated by logarithmic compression in the diodes 4, respectively.
The operation of the color temperatures sensor E will now be described. Light transmitted through the red color filter element 1R, for example, is incident on the photodiode 2R, and the photodiode 2R photoelectrically transfers the incident light into a photoelectric current. Specifically, the photoelectric current flows from a positive electrode of the constant voltage source 5 through the photodiode 2R and the diode 4 to the output terminal of the operational amplifier 3. Negative feedback is used in the operation amplifier 3 with the diode 4, so that the voltage difference between the noninverting input (+) and inverting input (-) is zero. Consequently, flow of the photoelectric current in the diode 4 causes a voltage drop, and a resultant voltage is obtained at the output terminal 6R. Thus, the photoelectric current, which is generated with the incident light transmitted through the red color filter element 1R, is transferred into the voltage compressed logarithmically, and the voltage is outputted from the output terminal 6R. Similarly, the photoelectric current, which is generated with the incident light transmitted through the green color filter element 1G, is transferred into the voltage compressed logarithmically, and the voltage is outputted from the output terminal 6G. Also, the photoelectric current, which is generated with the incident light transmitted through the blue color filter element 1B, is transferred into the voltage compressed lograithmically, and the voltage is outputted from the output terminal 6B.
In the conventional color temperature sensor E, the output voltages from the output terminals 6R, 6G, 6B are set using the repective color filter elements 1R, 1G, 1B. As a result, if the spectral characteristic of the color temperature sensor E is changed so as to obtain natural tone of color in a TV camera or to suit it to the characteristic of a camera device, for example, a novel color filter element having required filtering characteristic must be developed. For the development of such a novel color filter element, various characteristics of the color filter element such as heat resistance, light resistance, moisture resistance, vibration resistance and reliability (deterioration due to changes with time) must be evaluated while various investigations must be done. This requires a great deal of labor and development costs.